Test fixtures are utilized to removably retain an electronic circuit device or unit under test (UUT) in electrical communication with automatic test equipment (ATE). The ATE is operative to ascertain whether the UUT conforms to a predetermined standard of quality as well as functioning to provide a source of vacuum pressure for vacuum-operated test fixtures.
A vacuum-operated test fixture is structurally configured so that one side of the UUT is exposed to a vacuum condition while the other side is exposed to atmospheric pressure, the atmospheric pressure acting against the UUT to removably retain the UUT in physical contact with the test fixture, and consequently in electrical communication with the ATE. A typical prior art bed-of-nails vacuum-operated test fixture used for quality control testing of UUTs is shown in FIGS. 1A and 1B.
The bed-of-nails test fixture 10 of FIG. 1A includes a movable test head assembly 12 adapted to removably retain the electronic circuit device to be tested and an interface assembly 14 adapted to mechanically and electrically interface with the ATE. The UUT 16 is disposed adjacent a support structure 18 of the test head assembly 12, as shown in FIG. 1B. The surface of the UUT 16 facing the support structure 18 includes UUT test points 20.
The support structure 18 has a plurality of contact sockets 22 extending therethrough with the wire-wrap terminal portions thereof projecting from the surface of the support structure 18 distal the UUT 16. The plurality of contact sockets 22 correspond to the UUT test points 20 and contain spring-loaded contacts 24 which electrically engage the UUT test points 20 during vacuum operation of the test head assembly 12, i.e., when atmospheric pressure acts to force the UUT 16 against the support structure 18.
The interface assembly 14 includes a bottom pan 26 having an interface panel 28 affixed thereto. A plurality of interface contacts 30 are disposed to extend through the interface panel 28 such that the head portions thereof lie flush with one surface of the interface panel 28 and the wire-wrap terminal portions thereof project outwardly from the other surface of the interface panel 28. The head portions of the interface contacts 30 electrically interface with spring-loaded probes electrically connected to the ATE.
By moving the test head assembly 12 the bed-of-nails test fixture 10 may be positioned in an "open" or "closed" configuration. Testing of the UUTs 16 is accomplished with the test fixture 10 in the "closed" configuration wherein the test head assembly 12 is disposed within the bottom pan 26 of the interface assembly 14 such that the support structure 18 is parallel and superjacent to the interface panel 28. In the "closed" configuration the wire-wrap terminal portions of the contact sockets 22 and the interface contacts 30 are disposed in parallel proximity.
To complete the electrical test circuit between the test head assembly 12 and the spring-loaded probes electrically connected to the ATE, the wire-wrap terminal portions of the contact sockets 22 are hard wired to the wire-wrap terminal portions of the interface contacts 30 with the bed-of-nails test fixture 10 in the "open" configuration. In the "open" configuration the support structure 18 is disposed to lie in substantially perpendicular to the interface panel 28, as shown in FIG. 1A, such that there is a maximal separation between the wire-wrap terminal portions of the contact sockets 22 and the interface contacts 30.
Hard wiring is effected by wrapping first ends of interconnect wires 32 to the wire-wrap terminal portions of the contact sockets 22 and wrapping the second ends of the interconnect wires 32 to the wire-wrap terminal portions of the interface contacts 30. Hard wiring of the test fixture 10 in the "open" configuration necessitates the use of interconnect wires 32 which are relatively lengthy, having a length in the range of twelve to forty inches, due to the maximal separation between the wire-wrap terminal portions of the contact sockets 22 and the interface contacts 30.
The use of lengthy interconnect wires, however, creates relatively long signal paths between the UUT 16 and the ATE, a condition which is disadvantageous in real time testing of UUTs due to increased response time for the circuit. Additionally, long signal paths are generally high impedance paths which adversely affect the testing of UUTs because of unwanted capacitive, inductive and/or resistive effects.